Many polymeric surfaces, such as polyolefins, exhibit poor adhesion properties due to their low surface energy or polarity. For many applications, however, it is necessary to adhere a polymeric coating to a polyolefin surface in order to obtain desired overall properties.
Most reported methods for improving the adhesive strength of a polymer to a polyolefin surface involve modifying the properties of the polyolefin surface. These methods include chemical oxidation, flaming, plasma treatment, and grafting. Ref. S. Wu, "Polymer Interface and Adhesion", Marcel Dekker, New York, 1982, p.279. These surface treatments are used to change the chemical composition and increase the energy at the surface. Some chemical oxidation methods involve the use of chromic acid, potassium chlorate-sulfuric acid, potassium permanganate-sulfuric acid, nitric acid, sulfuric acid, alkyl peroxides, fluorine, chlorine and ozone.
J. Schultz, et al., J. Material Sci., 24, 4363-69 (1989) discloses modifying polypropylene by adding to the polypropylene a small quantity of polypropylene which has been grafted with a polar species such as maleic anhydride. Since the two polymers are compatible, the resultant polymer blend behaves like a bulk grafted polymer and leads to improved adhesion towards polar substrates.
Additives have also been added to an adhesive in order to promote adhesion to polyolefins such as polypropylene. Walker and Lombardi in Adhesives Age, Vol.33, No.8, 17-19 (1990) report improved adhesion of an acrylic emulsion between aluminum/polypropylene by blending in a polyurethane to the acrylic emulsion.